Packers for downhole use come in a variety of constructions. Some involve high ratios of expansion as between the set and the run in positions. These designs usually involve a collapsing petal shaped backup ring so as to control extrusion when the element is compressed axially over a stroke that is substantially longer than more conventional compression set packers. An example of such a design is U.S. Pat. No. 6,827,150. Other packer designs also address the extrusion issue as a result of setting the packer in a variety of ways, as shown for example in U.S. Pat. No. 5,941,313. Some packers use an element that can swell and expand a mandrel that lies beneath it, as illustrated in U.S. Pat. No. 6,834,725 and published application US 2004/0194971 A1.
One issue that arises with sealing elements that swell is that they get softer upon swelling and do not grip as firmly. Upon a change in well conditions such as temperature fluctuations or differential pressure variations, such set packers can lose their grip. In designs that do not involve mandrel expansion under a swelling element this is a concern for operators. Mandrel expansion increases the radial force on the swollen element but still leaves the issue of the swollen material being softer after swelling, which presents a risk of leakage or loss of grip. Swelling element packers are desirable in that they can be run in the well quickly and can assume a set position after leaving time to run them into position. Interaction with well fluids initiates the swelling to the point where sealing contact is obtained. It is advantageous to boost the sealing force of a swelling element in some way to better insure sealing integrity under a variety of conditions.
One approach to dealing with the sealing integrity concern can be seen in US 2005/0072579 in the context of a compression set packer. The variations disclosed in this reference deal with creation of potential energy in an element that is covered by the sealing element initially and which takes on a potential energy force when the sealing element that surrounds it is axially compressed. In one design the potential energy storing element is a swelling material disposed within the sealing element. These designs apply a very limited boost force by virtue of the positioning wholly under the sealing element and further dependence on movement of mandrel components that compress the element to additionally provide a potential energy force. The boosting device in this design is akin to a beam supported at opposed ends where the ends are pushed together to bend it. The middle of such a device can collapse due to lack of support if overloaded during setting or from the element due to changed conditions downhole.
Other references in the area of seals used in downhole applications are U.S. Pat. Nos. 6,923,263 and 5,851,013 as well as US Application 2005/0241833 and GB Applications 2,403,744 and 2,373,799.
The present invention addresses the need to boost the set of a swelling element in a variety of solutions. Preferably a cone shaped sleeve is driven axially in at least one direction adjacent at least one end of the swelling element so that preferably it can travel between the mandrel and the element and preferably have its motion locked in against reverse movement. These and other advantages of the present invention will be more apparent to those skilled in the art from a review of the description of the preferred embodiment and the associated drawings while the claims appended below denote the full scope of the invention.